MUNICH (AP) — The U.S. and Russia on Saturday finalized a nuclear arms treaty that limits the number of atomic warheads the former Cold War foes are allowed to possess — securing a key foreign policy goal of President Barack Obama.

The New START treaty was approved by the U.S. Senate in December after Obama pressed strongly for its passage, and Russia ratified the deal last month.

The treaty went into effect when U.S. Secretary of State Hillary Rodham Clinton exchanged the ratification papers with Russian Foreign Minister Sergey Lavrov on the sidelines of an international security conference in Munich.

New START is a cornerstone of Obama's efforts to "reset" U.S. relations with Russia.

Clinton said before the ceremony that the treaty is "another example of the kind of clear-eyed cooperation that is in everyone's interests."

In addition to New START, she said the U.S. is in talks with Russia about how the two countries can work together to address issues that affect their common security, while maintaining strategic stability.

Suggestions include joint analysis, joint exercises and sharing of early-warning data that could form the basis for a cooperative missile defense system, Clinton said.

She said she would also talk with Lavrov about "further arms control issues, including non-strategic and non-deployed nuclear weapons and our ongoing work to revive, strengthen and modernize the regime on conventional forces."

Lavrov called New START "a product of the understanding that unilateral approaches to security are counterproductive."

"The principles of equality, parity, equal and indivisible security ... form a solid basis for today's Russian-American interaction in a range of areas," Lavrov said.

"The treaty that enters into force today will enhance international stability."

The New START treaty, negotiated last year, limits each side to 1,550 strategic warheads, down from 2,200. The pact also re-establishes a monitoring system that ended in December 2009 with the expiration of an earlier arms deal.

U.N. Secretary-General Ban Ki-moon hailed the treaty's entering into force as "a historical, political milestone on the road to our ultimate goal: achieving a world free of nuclear weapons."

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